Moistureproofing of nonfibrous cellulosic material



Patented Aug. 25, 1953 MOISTUREPRO OFING OF NONFIBROUSE CELLULOSIC MATERIAL W lliam] 0. Brillhart, Signor to American mington, Del., a cor Fredericksburg, Viscose Corporation, Wilporation of Delaware:

Va., as-

No Drawing. Application January 21, 1949 Serial No. 72,065

This invention relates to improvements in non-fibrous cellulosic articles. More particularly it relates to the treatmentof regenerated cellulose sheets or films with an aqueous alkaline medium containing an anchoring agent for filmforming surface coatings whereby slightly alkaline sheets or filmswhich are not embrittled by age, and to which the surface coating firmly adheres, are obtained.

It is desirable, in the manufacture of sheets and films of hydrophilic cellulosic materials, i

such as regenerated cellulose and cellulose ethers and esters containing free hydroxyl groups, to provide the sheets and films with a surface coating for improving certain characteristics of the cellulosic article, such as its moistureproof, vapor proof, and/or heat sealing characteristics. A number of substances ,and compositions have been proposed for this purpose. However, it has been recognized that when the treated sheets are used to package materials of high moisture content, or come in contact withan atmosphere of high humidity or a medium actually containing liquid water, the cellulosic base tends to swell, and the surface coating tends to loosen and slough off. A number of different materials have been proposed for use as an intermediate anchoring agent between thehydrophilic cellu: lose and the surface coating. Some of these anchoring agents have had the disadvantage that they are acidic or revert to an acidic condition when the cellulosic article is dried after it has been treated with them. This is undesirable because cellulosic articles which comprise an acid tend to become brittle and fragile on ageing due to acid degradation of thecellulose. Such articles cannot be stored safely for any appreciable period of time. In order to avoid this difliculty it is necessary to treat the article, after application cfthe anchoring agent, to bring it to neutral or alkaline condition. y

Other anchoring agents havehad the disad vantage that they mustbe applied from organic solvents, entailing expensive solvent recovery processes. i

The principal object of this invention is to produce cellulosic articles, for example sheets or films, which are slightly alkaline as produced, and which can be given a topor surface coating of a film-forming substance or composition which imparts moistureproof, vapor proof, and/or heat-sealing characteristics to the cellulosic article, whereby the, surface coating is firmly anchored to the cellulosic article andis resistant to loosening or sloughing 01f when the article is exposed to moisture Another object is to provide an improved method for conditioning cellulosic articles forreception of a surface or top coating wherein the anchoring age nt is applied from aqueous alkaline medium. Another object 12 Claims. (01. 11776) is to produce cellulosic articles which adhere firmly to film-forming moistureproofing agents or compositions in contact with moisture and which do not become brittle with use or on long storing either before or after application of the moistureproofing agent. Other objects of the invention are to provide a simple, practical method of applying an anchoring agent to cellulosic articles from an alkaline solution which does not require any change in conventional processes for manufacturing such articles. Other objects will appear hereinafter.

The objects of the invention are accomplished by treating cellulosic articles such as sheets, films, pellicles, tubes, filaments, etc., with aqueous alkaline medium containing a resin comprising a polymerization product of styrene and maleic anhydride containing 50 mol per cent of styrene in the polymer molecule, in the form of a water-soluble salt of an alkaline agent selected from the group consisting of ammonia and amines having up to four carbons, and thereafter heating the treated cellulosic article to dry the article and insolubilize the resin under controlled conditions such that the amount of alkaline agent such as the amine or ammonia volatilized during the heating and insolubilizing step is not sufficient to effect conversion of the resin to the free acid state. In this Way, cellulosic articles which are slightly alkaline are obtained.

The cellulosic articles may be of regenerated cellulose prepared from solutions of cellulose xanthate or cuprammonium cellulose, or they may be of a cellulose ester orether, such as cellulose acetate, cellulose nitrate, ethyl cellulose, methyl cellulose, etc. which materials contain free hydroxyl groups and are hydrophilic in character.

In the preferred embodiment of the invention, an ammonium or amine salt of the styrenemaleic anhydride polymerization product is incorporated directly in the aqueous softening bath, such as theglycerol bath, on the casting machine for producing regenerated cellulose sheets, and thus the anchoring agent is applied to the gel sheet as it passes through the glycerol bath, after the sheet has been purified and washed, while it is in substantially neutral, Water-laden condition, and prior to initial drying thereof.- The sheet is then dried under controlled conditions of time and temperature such that the styrene-maleic anhydride polymerization product iS insolubilized without sufficient evolution of ammonia or amine to convert the anchoring agent to the acid condition. This curing of the resin without reversion thereof to the free acid state is accomplished by drying the impregnated sheet orfilm and simultaneously curing the resin ,atrelatively low temperatures ofL50-80i. C. ,for a short period of from 1 to 5 polymerization product to an acid condition, and then applying to the article a film-forming moistureproofing agent.

as in claim 1 wherein the aqueous alkalme medium also contains a quaternary ammonium salt as a catalyst for said insolubilization.

3. A method as in claim 1 wherein the aqueous alkaline medium also contains 4. A method for the production of a moistureproof cellulosic article which comprises applying to a hydrophilic cellulosic article, while it is in materials, said anchoring agent being a water-soluble salt of a medium, ture of from 50 to 80 to dry the article and 5. A method as in claim 4 wherein the cellulosic article comprises regenerated cellulose.

6. A method as in claim 4 wherein the cellulosic article comprises regenerated cellulose and the aqueous alkaline medium also contains a plasticizing agent for the cellulose.

7. A method as in claim 4 wherein the cellulosic article comprises regenerated cellulose and the aqueous alkaline medium also contains glyclosic article comprises regenerated cellulose and the aqueous alkaline medium also contains a the aqueous alkaline medium also contains a plasticizer for the cellulosic article and a quaternary ammonium salt as a catalyst for said insolubilization.

10. A composite film comprising a cellulosic base, a moistureproof coating, and, disposed between the base and the moistureproof coating, an

ated cellulose.

12. A composite film as defined in claim 11 wherein the sheet of regenerated cellulose is plasticized with glycerol.

WILLIAM O. BRILLI-IART. References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,976,679 Fikentscher et a1. Oct. 9, 1934 2,047,398 Voss et a1 July 14, 1938 2,168,535 Nuesslein et a1 Aug. 8, 1939 2,252,091 Muller et a1 Aug. 12, 1941 2,327,760 Bestian et a1 Aug. 24, 1943 2,341,413 Pense et a1 Feb. 8, 1944 2,356,879 Pense et al Aug. 29, 1944 2,394,009 Pollard Feb. 5, 1946 2,432,542 RitZl Dec. 16, 1947 2,467,436 Lanning Apr, 19, 1949 2,469,407 1 Powers et al. May 10, 1949 2,469,408 Powers et al May 10, 1949 2,469,409 Powers et a1 May 10, 1949 2,486,804 Seynor et al Nov. 1, 1949 FOREIGN PATENTS Number Country Date 466,817 Great Britain June 7, 1937 497,335 Great Britain Dec. 15, 1938 

1. IN THE PRODUCTION OF CELLULOSIC ARTICLES THE IMPROVEMENT WHICH COMPRISES APPLYING TO THE ARTICLE WHILE IT IS IN THE FORM OF A WET GEL PRIOR TO INITIAL DRYING THEREOF AS A STEP IN ITS MANUFACTURE, AN AQUEOUS ALKALINE MEDIUM CONTAINING A WATER-SOLUBLE SALT OF A POLYMERIZATION PRODUCT OF STYRENE AND MALEIC ANHYDRIDE CONTAINING ABOUT 50 MOL PER CENT OF STYRENE IN THE POLYMER MOLECULE, SAID SALT BEING FORMED WITH AN ALKALINE AGENT SELECTED FROM THE GROUP CONSISTING OF AMMONIA AND AMINES HAVING UP TO FOUR CARBONS, REMOVING EXCESS TREATING MEDIUM, AND THEREAFTERHEATING THE CELLULOSIC ARTICLE UNDER CONTROLLED CONDITIONS OF TEMPERATURE AND TIME TO DRY THE ARTICLE AND INSOLUBLIZE THE POLYMERIZATION PRODUCT WITHOUT VOLATILIZING SUFFICIENT ALKALINE AGENT TO CONVERT THE POLYMERIZATION PRODUCT TO AN ACID CONDITION, AND THEN APPLYING TO THE ARTICLE A FILM-FORMING MOISTUREPROOFING AGENT. 